1. Field of the Invention
The present invention relates to a component of a display device, and more particularly to a color filter substrate and a fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing static electricity on the color filter substrate.
2. Description of the Related Art
In general, a liquid crystal display device controls the light transmittance of liquid crystal using an electric field across a layer of liquid crystal molecules between two substrates to display a picture. The liquid crystal display device uses cells in an active matrix in which a switching device is formed in each of the cells. Liquid crystal display devices are used as display in televisions, computer monitors, office equipment, and cellular phones.
Liquid crystal display devices can be classified as either a vertical electric field type in which a vertical direction electric field extends between the two substrates or a horizontal electric field type is which a horizontal direction electric field extends across the surface of one of the two substrates. The vertical electric field type liquid crystal display device can drive a liquid crystal of TN (twisted nematic) mode with a vertical electric field between a common electrode on an upper substrate and a pixel electrode on a lower substrate. The vertical electric field type liquid crystal display device has an advantage in that the aperture ratio is high, but on the other hand, it also has a disadvantage in that the viewing angle is narrow, about 90°. The horizontal electric field type liquid crystal display device drives a liquid crystal of IPS (in-plane switch) mode with a horizontal electric field between a pixel electrode and a common electrode, which are formed in parallel on a lower substrate. The horizontal electric field type liquid crystal display device has an advantage in that the viewing angle is wide, about 160°, but on the other hand, it also has a disadvantage in that the aperture ratio is low.
FIG. 1 is a cross-sectional view representing a horizontal electric field type liquid crystal display device of the related art. As shown in FIG. 1, the horizontal electric field type liquid crystal display device includes a color filter substrate, a thin film transistor substrate and liquid crystal (not shown) injected into a gap between the substrates. The color filter substrate has a black matrix 4, a color filter 6, an overcoat layer 8, a spacer 13 and an upper alignment film 12 sequentially formed on an upper glass substrate 2. Further, a transparent electrode (ITO) 3 for preventing static electricity is formed on the other side of the glass substrate 2 of the color filter substrate. The thin film transistor substrate has a thin film transistor, a common electrode 10, a pixel electrode 56 and a lower alignment film 52 formed on a lower glass substrate 32.
The black matrix 4 of the color filter substrate overlaps the thin film transistors, gate lines (not shown) and data lines (not shown) of the lower glass substrate 32, and defines cell areas where color filters 6 are later formed. The black matrix 4 prevents light leakage and increases contrast ratio by absorbing external light. The color filters 6 are formed within the cell areas defined by the black matrix 4. The color filters 6 are red, green, and blue colored filters to realize red, green and blue colors.
The overcoat layer 8 covers a step difference formed by the color filter 6 to level the upper substrate 2. The spacer 13 maintains a cell gap between the upper and lower glass substrates 2 and 32. The spacer 13 can be simultaneously formed of the same material as the overcoat layer 8. The upper alignment film 12 is formed on the overcoat layer 8 where the spacer 13 is formed and initially aligns liquid crystal molecules interposed between the thin film transistor substrate and the color filter substrate in a designated direction. The lower alignment film 52 is formed on the passivation film 50, which covers the thin film transistor, and initially aligns the liquid crystal molecules interposed between the thin film transistor substrate and the color filter substrate in the designated direction.
The thin film transistor of the thin film transistor substrate includes a gate electrode 38 formed on the lower glass substrate 32 together with the gate line (not shown); a semiconductor layer 93, which overlaps the gate electrode 38 with the gate insulating film 34 therebetween; a source electrode 46 and a drain electrode 48. Contact semiconductor layers 92 reduce the contact resistance between the semiconductor layer 93 and each of the source and drain electrodes 46 and 48. In response to a gate signal from the gate line, a thin film transistor applies a pixel signal from the data line to the pixel electrode 56, which is connected to the drain electrode 48 through a contact hole in the protective passivation film 50.
The common electrode 10, which is a stripe type alternating with a pixel electrode 22, is simultaneously formed on the lower glass substrate 32 along with the gate line. A reference voltage that serves as a reference voltage upon driving of the liquid crystal 24 is supplied to the common electrode 10 through the common line. A horizontal electric field is formed between the pixel electrode 56 to which a pixel signal is supplied through the thin film transistor and the common electrode 10 to which a reference voltage is supplied through the common line. The horizontal electric field causes the liquid crystal molecules, which are initially arranged in a horizontal direction between the thin film transistor substrate and the color filter substrate, to rotate in a designated direction so as to change the light transmittance through the liquid crystal molecules, thereby realizing a picture.
FIGS. 2A to 2I illustrate a process of forming a color filter substrate for a horizontal electric field type liquid crystal display device of the related art. As shown in FIG. 2A, a static electricity prevention transparent conductive film ITO 3 is formed by a sputtering method on the glass substrate 2. More specifically, a high RF (DC) power is applied to a target opposite to the glass substrate 2, both of which are within a chamber filled with argon Ar gas. Ar molecules having a high energy in the plasma formed by the RF (DC) power lose (−) charge and collide with the target surface in an Ar+ state so that target particles come out of the target and are deposited onto the glass substrate 2, thereby forming the transparent conductive film (ITO) 3 for preventing static electricity buildup, as shown in FIG. 2B.
After forming the transparent conductive film 3 for preventing static electricity buildup, the black matrix 4 is formed on the glass substrate 2 to prevent light leakage. More specifically, an opaque material is spread on an other side of the glass substrate 2 opposite to the side of the glass substrate where the transparent conductive film 3 was formed. The opaque material is an opaque resin or an opaque metal, such as chrome Cr. Next, the opaque material is patterned by a photolithography process using masking and etching processes, thereby forming the black matrix 4, as shown in FIG. 2C. Red, green, and blue color filters are formed in cell areas defined by the black matrix after forming the black matrix 4.
Specifically, a red photo-sensitive color resin is deposited over the entire surface of the glass substrate 2 on which the black matrix 4 is formed. Next, the red photo-sensitive color resin is patterned by a photolithography process using masking and etching processes, thereby forming a red color filter R, as shown in FIG. 2D.
After forming the red color filter, a green photo-sensitive color resin is then deposited over the entire surface of the glass substrate 2 on which the red color filter R is formed. Then, the green photo-sensitive color resin is patterned by a photolithography process using masking and etching processes, thereby forming a green color filter G, as shown in FIG. 2E.
After forming the green color filter, a blue photo-sensitive color resin is deposited over the entire surface of the glass substrate 2 on which the red and green color filters R and G are formed. Then, the blue photo-sensitive color resin is patterned by the photolithography process using masking and etching processes, thereby forming a blue color filter B so as to complete the color filters 6, as shown in FIG. 2F.
Subsequently, the overcoat layer 8 for providing a planar surface is formed, as shown in FIG. 2G, after forming the R, G, B color filters 6. More specifically, an organic insulating material is coated over the entire surface of the glass substrate 2 on which the color filters 6 are formed. Then, the organic insulating material is patterned by a photolithography process using a masking and an etching process, thereby forming the overcoat layer 8 having a planar surface over step differences formed by the color filters 6.
After forming the overcoat layer, a spacer 13 is then formed for maintaining a cell gap between the thin film transistor and the color filter substrate, as shown in FIG. 2H. More specifically, the same organic insulating material used for forming the overcoat layer 8 is coated over the entire surface of the glass substrate 2 on which the overcoat layer 8 is formed. Then, the organic insulating material is patterned by a photolithography process using masking and etching processes, thereby forming the spacer 13 to maintain the cell gap, as shown in FIG. 2H.
After forming the spacer 13, an alignment film 12 for initially aligning liquid crystal molecules in a designated direction is formed over the surface of the glass substrate 2 on which the spacer 13 is formed, as shown in FIG. 2I, thereby completing the color filter substrate.
In the related art, in the case of forming the color filter substrate by the fabrication process described above, the transparent conductive film (ITO) 3 on the rear surface of the glass substrate 2 is formed by a sputtering process, which is a complicated process step that requires a large amount of time. Further, in the case of forming the color filter substrate of the related art with a transparent conductive film 3 on the rear surface of the glass substrate 2, there is a problem in that it is impossible to make the color filter substrate light and thin because the glass substrate 2 can not be etched after the black matrix, the color filter, the overcoat layer and the alignment film are formed on the other side of the glass substrate when the transparent conductive film 3 is on the rear surface of the glass substrate 2.